This invention relates generally to magnetic disk drives, and more particularly to spin valvexe2x80x94giant magnetoresistive (GMR) thin film read heads.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatus such as computers. In FIGS. 1A and 1B, a magnetic disk drive D of the prior art includes: a sealed enclosure 1; a disk drive motor 2; a magnetic disk 3 supported for rotation by a spindle S1 of motor 2; an actuator 4; and an arm 5 attached to a spindle S2 of actuator 4. A suspension 6 is coupled at one end to the arm 5, and at its other end to a read/write head or transducer 7. The transducer 7 is typically an inductive write element with a sensor read element. As the motor 2 rotates the disk 3, as indicated by the arrow R, an air bearing is formed under the transducer 7 to lift it slightly off of the surface of the disk 3. Various magnetic xe2x80x9ctracksxe2x80x9d of information can be read from the magnetic disk 3 as the actuator 4 is caused to pivot in a short arc as indicated by the arrow P. The design and manufacture of magnetic disk drives is well known to those skilled in the art.
The most common type of sensor used in the transducer 7 is the magnetoresistive sensor. A magnetoresistive (MR) sensor is used to detect magnetic field signals by means of changing resistance in a read element. A conventional MR sensor utilizes the anisotropic magnetoresistive (AMR) effect for such detection, where the read element resistance varies in proportion to the square of the cosine of the angle between the magnetization in the read element and the direction of a sense current flowing through the read element. When there is relative motion between the MR sensor and a magnetic medium (such as a disk surface), a magnetic field from the medium causes a change in the direction of magnetization in the read element, thereby causing a corresponding change in resistance of the read element. The change in resistance can be detected to recover the recorded data on the magnetic medium.
Another form of magnetetoresistance is known as spin valve magnetoresistance or giant magnetoresistance (GMR). In such a spin valve sensor, two ferromagnetic layers are separated by a non-magnetic layer such as copper. One of the ferromagnetic layers is a xe2x80x9cfreexe2x80x9d layer and the other ferromagnetic layer is a xe2x80x9cpinnedxe2x80x9d layer. This pinning is typically achieved by providing an exchange-coupled anti-ferromagnetic layer adjacent to the pinned layer.
More particularly, and with reference to FIG. 1C, a shielded, single-element magnetoresistive head (MRH) 10 includes a first shield 12, a second shield 14, and a spin valve sensor 16 disposed within a gap (G) between shields 12 and 14. An air bearing surface S is defined by the MRH 10. The spin valve sensor is preferably centered within the gap G to avoid self-biasing effects. Lines of magnetic flux impinging upon the spin valve sensor create a detectable change in resistance. The design and manufacture of magnetoresistive heads, such as MRH 10, are well known to those skilled in the art.
With reference to FIG. 2A, a cross-sectional view taken along line 2xe2x80x942 of FIG. 1C illustrates the structure of the spin valve sensor 16 of the prior art. The spin valve sensor 16 is built upon a substrate 17 and includes: an anti-ferromagnetic layer 24; a pinned layer 22; a first cobalt enhanced layer 19; a thin copper layer 20; a second cobalt enhanced layer 23 and a free layer 18. Ferromagnetic end regions 21 abut the ends of the spin valve sensor 16. Leads 25, typically made from gold or another low resistance material, bring the current to the spin valve sensor 16. A capping layer 27 is provided over the free layer 18 opposite the Co enhanced layer 23. A current source 29 provides a current Ib which flows through the various layers of the sensor 16, and signal detection circuitry 31 detects changes in resistance of the sensor 16 as it encounters magnetic fields.
The free and pinned layers 18 and 22 are typically made from a soft ferromagnetic material such as Permalloy. As is well known to those skilled in the art, Permalloy is a magnetic material nominally including 80% nickel (Ni) and 20% iron (Fe). While the layer 20 is typically copper, other non-magnetic materials have been used as well. The cobalt enhanced layer can be preferably constructed of Co or more preferably of Co90Fe10. The AFM layer 24 is used to set the magnetic direction of the pinned layer 22.
With continued reference to FIG. 2A, the spin valve sensor 16 develops a rough interface between the copper layer 20 and the cobalt enhanced layer 23. This can be understood better with reference to FIG. 2B, wherein the interface is shown at the atomic level. Both the copper layer 20, shown in solid, and the cobalt enhanced layer 23 have face centered cubic (FCC) crystalline structures. However, as the copper is deposited onto the first cobalt enhanced layer 19, the copper tends to form in groups or xe2x80x9cislandsxe2x80x9d rather than being deposited layer by layer as would be desired. This leads to a rough copper surface upon which the second must subsequently be deposited. Therefore, the interface 30 between the copper spacer layer and the second cobalt enhanced layer 23 takes on this rough texture as shown in FIG. 2A.
With reference to FIGS. 3A and 3B, the free layer 18 can have a magnetization vector 26 which is free to rotate about an angle xcex1, while the pinned layer 22 is magnetized as indicated by the arrow 28. Absent the influence of a magnetic field, such as that provided by a magnetic recording medium, the magnetization of the free layer, as represented by arrow 30, would ideally be perpendicular to the direction of the magnetization 28 of the pinned layer 28. However, when the free layer is subjected to a magnetic field, represented by arrow 32, the resulting magnetization 26 of the free layer becomes the sum of the magnetic flux magnetization 32 and the magnetization 30. It is a property of GMR heads that as the angle xcex1 changes, the resistance of the sensor 16 will change. The relationship between the angle xcex1 and the resistance of the sensor will be essentially linear in the region of xcex1=0 degrees (i.e. when vector 26 is approximately perpendicular to vector 28. This can be seen with reference to FIG. 3B.
With reference to FIG. 3C, a GMR read element 10 which does not have an initial angle xcex1 which is substantially equal to zero in the absence of any external magnetic field will experience errors when reading data. A typical magnetic recording medium records data as a series of magnetic pulses in the form of waves. The sensor reads these waves and generates a signal having a sensor output, i.e. Track Average Amplitude (TAA). As can be seen with reference to FIG. 3C, a positive magnetic pulse results in an output amplitude TAA1 followed by an equivalent negative pulse resulting in a sensor output amplitude TAA2 of the same absolute value. If a read sensor 10 has an initial magnetization angle xcex1 of zero then the read sensor will be able to detect these opposite pulses as such. However, if the angle is substantially greater than or less than zero the read sensor will impart an offset error which will cause the sensor to read one of the pulses as being larger than it actually is and the other as being smaller. In such a case, the sensor may not register the smaller pulse and may miss that bit of data. The tendency of read heads to impart such an offset error is termed Track Average Amplitude Asymmetry (TAAA) and is defines as (TAA1xe2x88x92TAA2)/(TAA1+TAA2). A TAAA of less than 15% is generally required for a read head to function properly.
With brief reference to 3A, in order for xcex1 to equal 0 in the free state, several magnetic forces acting on a magnetization vector 26 of the free layer 18 must balance to 0. In FIG. 3D, Hd represents a demagnetization vector. Demagnetization can be controlled by adjusting the thickness of the pinned layer 22. This Hd is offset by an interlayer magnetic coupling field Hint and a current induced magnetic field Hi. Hi is controlled by the bias current Ib and is generally set by design considerations external to the head 10 itself. Correct operation of the head 10 requires that the these three magnetic field vectors: Hd, Hint and Hi sum to 0.
With reference to FIG. 4 Hint, is dependent upon the thickness tcu (FIG.2A) of the copper layer. The thickness of the copper layer is desirably chosen so that Hint will be 0. Furthermore, the sensitivity of the sensor (xcex94r/r) increases with decreasing copper layer thickness. Therefore, the copper layer is preferably chosen to have a thickness corresponding to node 34 in FIG. 4. However, as indicated by the steep slope of the curve in region 34, Hint changes drastically with copper spacer thickness in this region. In fact a single angstrom change in copper layer thickness can have a substantial impact upon Hint. Therefore, control of copper layer thickness is critical in the design and production of GMR heads. However, as will be appreciated, any roughness in the interface between the copper layer and adjacent magnetic layers will render such copper layer thickness variable across the surface of the copper layer.
Another problem experienced by GMR heads, is that of diffusion at high temperatures. Migration of atoms across the interface between the copper layer and the adjacent magnetic layers results in degradation of performance. This is especially a problem when the sensor is subjected to high temperatures. It has been discovered that roughness of the interface contributes greatly to such diffusion.
Therefore, there remains a need for a GMR sensor and a method of manufacturing the same which will allow a smooth interface between the copper layer and adjacent pinned and free magnetic layers. Such a GMR head would achieve the benefit of tighter control of copper layer thickness as well as reduced diffusion of atoms across the interface.
The present invention provides a spin valve sensor having improved performance, reliability and durability and a method of manufacturing same. The spin valve includes a copper layer separating first and second magnetic layers disposed adjacent the copper layer. The spin valve achieves the above described beneficial results by maintaining a very smooth interface between the copper layer and the adjacent magnetic layers. An anti-ferromagnetic (AFM) layer fixes the magnetization of a pinned layer. The spin valve also includes a free layer having a magnetization which can move under the influence of an external magnetic field. Changes in relative orientation of magnetizations between the free and pinned layers cause measurable changes in the resistance of the spin valve.
By providing improved interfaces between the copper layer and adjacent magnetic layers, the copper layer thickness can be precisely controlled. This results in the ability to precisely control the relative magnetization angles between the free and pinned layers. Furthermore, such a smooth interfaces maximize xcex94r/r performance. These improved interfaces between the copper and adjacent magnetic layers also act to prevent inter layer diffusion of atoms which would degrade performance of the spin valve, especially at high temperatures, and would decrease the life of the spin valve.
More particularly, the spin valve includes a substrate upon which the spin valve is built. This substrate may be, for example, ceramic. The AFM layer is deposited onto the substrate and the pinned layer is subsequently deposited onto the AFM layer. The pinned layer can be preferably constructed of Co or more preferably of Co90Fe10.
An ultra thin layer of lead is deposited onto the pinned. layer. This layer of lead is preferably no more than two or three atoms thick and most preferably is no more than a single atom thick. With the lead deposited onto the pinned layer, a copper layer is then deposited onto the lead. The presence of the lead serves as a surfactant, causing the copper atoms to move to the desired location, growing layer by layer in a face centered cubic structure. As the copper is deposited, the lead rises to remain on the top of the deposited copper layer. The lead continues to migrate as the spin valve is formed, so that when the spin valve is completed, no detectable trace of the lead remains.
The layer by layer growth of the copper layer provides a smooth surface on which to deposit a cobalt (Co) enhanced layer. The Co enhanced layer preferably consists of Co90Fe10. The free magnetic layer is then deposited onto this Co enhanced layer.
Thereafter, ferromagnetic end regions are provided at the ends of the spin valve so as to span across the various layers of the spin valve. A pair of leads are also provided to allow a bias current to be fed through the spin valve.
The improved interface provided between the copper layer and the adjacent layers allows the copper layer thickness to be tightly controlled, thereby improving sensor performance and reliability. Furthermore, these improved interfaces prevent interlayer diffusion, also as discussed above.
These and other advantages of the invention will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawing.